Multidentate ligand exchange kinetics: Substitution reaction of polyaminocarboxylatoferrate (III) complex, [FeHPDTA(OH)]2− with 4‐(2‐pyridylazo)resorcinol

Abstract

AbstractThe kinetic study of ligand substitution reaction of 2‐hydroxy 1,3‐diamino propane N,N′N′‐tetraacetatoiron(III) ([FeHPDTA(OH)]2−) complex with 4‐(2‐pyridylazo)resorcinol (Par) has been followed spectrophotometrically at pH = 9.00 ± 0.02, I = 0.1 M (NaClO4), and temperature = 25.0 ± 0.1°C. The forward and reverse reactions have been studied at 496 nm, the λmax of [Fe(Par)2]− which is identified as the final product of above reaction. The second‐order rate constants for the reaction of [FeHPDTA(OH)]2− with Par were determined in a wide pH range viz. 8.0–11.5. It is observed from pH dependence of reaction that rate of reaction increases initially with pH and then levels off. In the case of reverse reaction between [Fe(Par)2]− and HPDTA4−, the pseudo‐first‐order rate constant does not change with concentration at extremely low concentration of [HPDTA]4− and shows zero‐order dependence in [HPDTA]4−. At relatively higher concentration of [HPDTA]4−, the order of reaction with respect to [HPDTA]4− is found to be 1. An inverse first‐order dependence is also observed with respect to added [Par]2−. The activation parameters were evaluated for forward and reverse reactions, which further supported the proposed mechanistic scheme. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 333–340, 2005